Cable networks have been traditionally used to transmit video to users through their cable set-top boxes. The transmissions originate at a head-end, generally at a central location provided by the cable network provider. The transmission is received at the user end by a cable set-top box.
Using the infrastructure already established for the cable network, cable network providers began providing data services to users. With the use of a cable modem, users can transmit and send data across the network to other networks, such as packet-based networks like the Internet. The transmission travels upstream from the cable modem to the head-end, or a hub, where it is terminated by a cable modem termination server (CMTS). The CMTS then transmits the data out of the hub or head end to the packet network.
The CMTS also transmits the data from the packet network to the cable modem. The transmissions are generally across channels established within the spectrum available for transmissions. The channels are quadrature amplitude modulation channels (QAM), sometimes referred to as QAMs or narrow-band channels.
It is possible to create a higher bandwidth channel by grouping several QAMs together. Essentially, the higher bandwidth channel, sometimes referred to as a wideband or bonded channel, is an overlay on the narrow-band QAMs. This allows the existing narrow-band infrastructure to be used for wideband transmissions. The data is transmitted in bundles across the QAMs. In order to implement this type of scheme, however, the downstream equipment needs a means to reconstruct the transmissions.